Why the 3d sound of my object stays the same in bge?
In the sound actuator set: minimun gain to 0.0, maximun gain to 1.0 and maximun distance to ~50 (estimate from the image provided), i dont know the scales you are using but the camera appear to be at ~50 units from the sound position. The scales of your blend are weird so is dificult to say something near reallity.

Here is a .blend to demonstrate, just press P and then SPACE to move the camera.